air compressor size????

Ok according to this
http://www.jennyproductsinc.com/howtochoose.html
You need 11 - 13 cfm to run a dual action sander. They say to add 30% so that brings it up to 14.3 - 16.9 cfm to run a DA continuously. I think the 30% is a little high but the link above has some good buying info even though it is a little biased.
That DA is one air hungry tool that get used for long stretches at a time.